Processes for causing an extensible polymer film to adhere to the edge of the opening of a bottle or similar container made of plastic (pet or the like) or metal and various devices for implementing said processes

ABSTRACT

Various processes and relevant devices for causing polymer films, which are extensible to adhere to the edges of openings of plastic or PET or even metal containers, by releasing electrostatic charges opposite in sign to those of containers and/or the polymer films to be applied thereto. The processes derive from a single general inventive concept.

This application claims the benefit of Swiss Application No. 1059/01filed Jun. 13, 2001 and PCT/IB02/02132 filed Jun. 11, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of container closures andparticularly of liquid and food container sealing. It addresses twoprocesses to condition both the edge of the opening of the plastic ormetal container and the extensible polymer film to be applied theretowith the process disclosed in Patent Application Ribi WO 98/32668 ofJan. 23, 1998.

Thanks to such conditioning, performed with various devices allowing toperform the processes, an effective and safe sealing effect is obtained.

2. Related Art

In prior art sealing techniques, liquid and/or food containers aretypically sealed either by means of bonded screw plugs or metal plugs,or by the application of various metal disks, to be attached to the edgeof the opening, or with blind seals, which are held in position by othermechanical devices, like those mentioned above.

A more practical, cost-effective, hence industrially advantageousarrangement is proposed by the invention disclosed in Patent ApplicationWO 98/32688 of Jan. 23, 1998, and various implementations thereof, i.e.devices for applying extensible polymer films to the edges of theopenings of glass containers.

Nevertheless, this arrangement cannot be used for plastic or metalcontainers because, as explained below, adhesion thereof is hindered bythe electrostatic charges of equal polarity on the faces of the twomaterials to be attached or simply due to the lack of electric chargeson said faces.

SUMMARY OF THE INVENTION

The processes which form the subject of this invention and the devicesused for implementation thereof allow two plastic surfaces, or plasticand metal surfaces, to effectively adhere to each other, therebyassisting the application of an extensible polymer film to the openingof a plastic or metal container.

The invention essentially consists in charging electrostatically theadhering surfaces in opposite polarity and in possibly improving saidadhesion by heating the two surfaces.

The tight adhesion of extensible plastic seals on plastic or metalmaterials not only depends on the surface condition, but also ontemperature, which allows a better mutual adaptation of the twomaterials in contact with each other during the application.Nevertheless, as shown in various tests and specific measurements, filmadhesion is mostly affected by the presence of opposite electrostaticcharges on the opposed faces of the materials to be attached.

Typically, in normal conditions, the charges on the two materials, i.e.plastic-plastic or plastic-metal, unlike glass-plastic, have the samepolarity (or are absent), hence the surfaces tend to remain separatewhen attempting to join them.

The processes of this invention, and the devices used to implement them,consist in assigning electrostatic charges of opposite polarity to thetwo adhering materials.

This simple arrangement allows even a relatively weak force, likeelectrostatic force, to be effective in assisting the adhesion of thedeformable extensible plastic material to the edge of the containeropening, so that the two boundary air layers adjacent to the twomaterials are removed thereby allowing atmospheric pressure to exert itsfull force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b show the device in its simplest configuration forimplementing the process adhering two surfaces.

FIG. 2 shows the device of FIGS. 1 a and 1 b including a generator andaccessories thereof.

FIG. 3 shows the device with a single capacitor.

FIG. 4 shows the device applying film to a metal can.

DETAILED DESCRIPTION OF THE INVENTION

The process consists in directing a flow 24, or continuous ordiscontinuous jet of air or any appropriate dry gas on the edge of theopening 21 of the container 1 to be sealed.

This flow 24 is generated by any suitable compressed air or gas source,e.g. a compressor, or even directly by heating or changing the state ofa suitable liquid or solid. Obviously, this process is conceived for andoperates on any suitable surface composing the edge 21 of the containerto be sealed, either painted, anodized, frosted or passivated.

The typical device for the implementation of said basic process, asshown in FIG. 1 is described below.

In order to improve the efficiency of the process, the moleculescomposing the flow 24 are charged electrostatically by using anelectrostatic charge generator 8 equal or equipollent to the so-calledVan der Graaf type, with or without capacitors 9, to increase theavailable charges. Then, these charges are directly released to themolecules of the flow 24, by simple contact in the feed pipe 15.

So, the plates 7 of the same sign may be licked by the flow 24 therebysuitably charging it.

Various capacitors may be used, either simply consisting of two plates 7with an interposed dielectric 19, i.e. the air or gas itself, or formedby combinations of various plates with other interposed dielectrics 19.The plates 7 may also be made of porous materials to extend the surfacethereof, such as activated carbon, which may be also used with suitablefluid dielectrics 19.

The devices for implementing the above mentioned variants of theprocess, are described below.

The air or gas flow 24 is appropriately heated by electrical resistorsor any suitable heat exchangers 18 disposed in the feed pipe 15 or bythe pipe 15 itself, after suitably heating it, to bring the edge of theopening 21 and possibly also the film 13 of the seal to the propertemperature.

Obviously, heating temperature must not exceed the softening points ofthe materials in use.

Said heating assists the adhesion of the film 13 both for a betterplasticity of the contacting surfaces, and for the decreased viscosityof air or gas which form the boundary layer adjacent to the surfaces.

Typically, the process is effective because the boundary air or gaslayer of the surfaces is removed as the surfaces of the film 13 and theopening 21 are driven closer thanks to the electrostatic forces. Hence,atmospheric pressure, which is no longer counterbalanced by the pressureof residual air or gases between the two surfaces, can be fully exerted,thereby creating such a force of adhesion as to create in turn atangential, i.e. shearing friction between the two surfaces: whosecoefficient of friction, which increases with the plasticity or relative“adaptability” of the two surfaces, improves when the edge 21 of theopening and the film 13 are heated.

The device for implementing this variant of the process is describedbelow.

As an alternative to the previously described heating arrangement, theedge of the containers 21 and/or the film 13 which forms the seal arepreviously suitably heated by a radiant heat energy source 22.

The device for implementing this variant of the process is describedbelow.

The gas of the flow 24 is replaced by dry steam 27 produced by anyappropriate dry steam generator 25. This variant has the advantage thatthe edge of the container opening 21 is heated directly. In practice,the edge 21 is preferably pre-heated to a certain temperature, anywaybelow the material softening point by a heat source 22, to prevent anycondensation of dry steam 27.

A suitable monitored system for integrating and controlling flow rate,pressure, temperature and time of exposure to flow 27 allows adrawback-free optimized use of the device. Moreover, the dry steam jet27 will have the advantage of sterilizing the edge of the opening 21 ofthe container 1.

The device for implementing the above process, shown in FIG. 1 b isdescribed below.

The process consists in releasing by contact opposite electrostaticcharges to the edge of the opening 1 and to the film 13 to be appliedthereto.

This contact occurs before and during the step of applying the sealingfilm 13, whereas the charges of one sign are released by the containersupport 11 to the container 1 itself and the charges of the oppositesign are released by the film driving rollers 12 to the film 13. Chargesare usually provided by a special generator 8, possibly includingcapacitors 9 and rheostats 10.

The device for implementing this variant of the process, shown in FIG. 1b is described below.

The device as shown in FIG. 1 a, consists in a compressed air or gasgenerating system, in which compressed air or gas is generated by anysuitable pump 2, equipped with a motor 3. The system includes one ormore storage tanks, pipes 15 having opening and closing valves, flowcontrol valves and one or more nozzles 5 which may be oriented relativeto the opening of the container 21 to be sealed. Therefore, air or gasflow is controlled by manometers P and manostats PS, for controllingoutlet pressure, hence flow rate. This air or gas flow may also bepulsating and coincide with the passage of the container edge before thenozzle/s.

The jet has the function of removing and pushing away the electrostaticcharges of the container 1, or appropriate new electric charges, in sucha manner that a difference of electrostatic potential is establishedbetween the container 1 and the film 13 acting as a seal.

The force exerted by the electrostatic charges will allow air or gasesto be expelled from between the two surfaces, thereby allowingatmospheric pressure to exert its full force.

The device as shown in FIG. 2, consists of a system including anelectrostatic charge generating system. This system comprises a chargegenerator 8 of the “Van der Graaf” or equivalent type, one or moreappropriate capacitors 9 and at least one rheostat 10.

The equal sign plates of these capacitors 9, may be either connected toappropriately insulated surfaces in contact with the air or gas flow orbe themselves immersed in the gas carrying pipe 15. This sign shall beopposite to the one of the charges at the surface of the film 13.

The device as shown in FIG. 1, consists in a system which has scatteringtips 17 both on the surfaces in contact with the flow in the feed pipe15 and on the equal-sign plate/s of the capacitors 9, immersed in theflow.

These tips have the function of quickly releasing the capacitor chargesto air or gas. The concentration of charges on projections of chargedsurfaces is a well-known physical phenomenon.

In the device shown in FIG. 2, the plates 7 of the capacitors 9 areconnected to one or more additional homologous plates 7 of capacitors 9,even outside the feed pipe 15, and to one or more rheostats 10 whichhave the function to control the flow of electric charges to bereleased.

In the device shown in FIG. 2, the systems are equipped with a heatingsystem.

This system will be preferably inserted in a special widened portion ofthe feed pipe 15, i.e. a muffler 4 containing one or more heaters 18 ofany type, e.g. electric resistors or heat exchangers.

This system will obviously be monitored by appropriate thermostats TSand suitably insulated. An alternative to this solution consists inheating the feed pipe 15 by the same means.

The device shown in FIG. 1 b, consists in a system wherein the air orgas jet is replaced by a dry steam generating system. This systemconsists of a dry steam generator 25, with measuring and controllingequipment as well as with an adequately insulated feed pipe 15. Thecontrol equipment consists of automated thermostats TS and manostats PSand a flow controller R. Water may be advantageously heated electricallybut also by other sources of heat energy.

This device will be preferably used in association with a preheater 22for preliminarily heating the surfaces to be blown to preventcondensation. Moreover, dry steam 27 will have the function ofsterilizing the edge of the opening 21.

The device identical to the one provided for air or gas, supplements thedevice described above. Here, the dry steam blowing system integrates asystem for generating electrostatic charges and releasing them to watermolecules.

The inflow pipe 26 will have inner insulated surfaces connected to theequal-sign plates 7 of one or more capacitors, which are in turn fed byan electrostatic charge generator 8. The inner surfaces or plates 7 ofthe inflow pipe 26 may in turn have scattering tips 17, as in the caseof air or gas.

The charge flow will be controlled as needed by an appropriate rheostat10.

In the device shown in FIG. 3, a radiant heat source is used for anytype of device as described and claimed herein. This infrared raygenerating source may be either simply an electrically heated surface orany other heated mass in any other appropriate manner. Both parts, i.e.the container 1 and the film 13 will be placed in the proximity of thesurfaces to be headed in such a manner that radiant heat brings thecontainer opening 21 and the film 13 to the desired temperatures.

In the device which is not shown, a corona-type charge generator isused. An adequately insulated high voltage generator for chargingsuitable bodies disposed in the proximity of the edge of the opening 21and of the film 13, will release charges of the appropriate sign to thesurfaces. Then, the generator will typically consist of an electricgenerator, one or more high voltage transformers, appropriate controland adjustment instruments, like capacitors 9, rheostats 10, fuses andinsulated wires.

The device shown in FIGS. 3 and 4 consists of an electrostatic chargegenerating system which will supply both the container 1 and the filmwith electrostatic charges of opposite signs. The “Van der Graaf” orequivalent generator 8, equipped with rheostats 10 and one or morecapacitors, will feed, by the plates of opposite sign 7 of itscapacitor/s, the support 11 of the container on the one hand and thedriving rollers 12 for the film band 13. Hence, the opposite signcharges will cause the film 13 and the edge of the container opening 21to adhere against each other and will expel the residual air or gasbetween the two surfaces.

LIST AND KEY OF FIGURES

FIG. 1 a

Shows the device in its simplest configuration for implementing theprocess as claimed and comprises the following:

-   1. Plastic or metal container to be sealed.-   2. Gas pump (for air or other suitable gas).-   3. Motor.-   4. Storage tank.-   5. Nozzle.-   11. Container support (possibly movable, e.g. conveyor belt).-   12. Roller for driving the extensible polymer film (possibly    armor-plated).-   13. Extensible polymer film (possibly armor-plated).-   14. Device for applying the extensible polymer film (as per Patent    application WO 98/32668 of Jan. 23, 1998).-   15. Gas pipe.-   21. Opening edge.-   P. Manometer.-   S. Condensation drain.-   M. Flow control.-   PS. Manostat

FIG. 1 b

-   24. Gas flow pipe.-   25. Dry steam generator.-   26. Insulated pipe.-   27. Dry steam jet.-   TS. Thermostat.-   R. Flow control.-   M. Additional flow control.

FIG. 2

Shows the device in the configuration that includes a generator andaccessories thereof for implementing the process as claimed andcomprises the following:

-   1. Plastic or metal container.-   2. Gas (air) pump.-   3. Motor.-   4. Storage tank.-   5. Nozzle.-   6. Muffler containing capacitor plates immersed in the air flow.-   7. Plates of the internal capacitor.-   8. Generator.-   9. External parallel capacitor.-   10. Rheostat.-   11. Insulated support.-   12. Film driving roller.-   13. Polymer film.-   14. “RIBI” film application device.-   15. Gas pipe.-   16. Manostat electric contactor.-   17. Scattering tips.-   18. Heater.-   21. Opening edge.-   24. Gas flow pipe.-   P. Manometer.-   T. Thermometer.-   TS. Thermostat.-   M. Flow control.-   PS. Manostat.

FIG. 3

Shows the device with a single capacitor 9 for implementing the processas claimed and comprises the following:

-   1. Plastic (or metal) container.-   7/11. Container support.-   8. Generator.-   9. Capacitor.-   10. Rheostat.-   7/11. Container support (and plate).-   12. Film driving guide roller.-   12 bis. Film driving guide roller (and plate having a charge    opposite to the container support).-   13. Extensible polymer film.-   14. “RIBI” film application device.-   20. Insulator.-   21. Opening edge.

FIG. 4

Shows a device for applying the film 13 to a metal can 1, wherein boththe film driving roller/s 12 or 12 bis and the container support arethemselves capacitor plates, and consist of at least two plates, havinga dielectric 19 interposed therebetween, and whose charges, of oppositesign, are released to the film 13 and to the container 1. The drawingcomprises the following:

-   1. Container.-   8. Generator.-   9. Capacitor.-   10. Rheostat.-   7./11. Support-plates.-   12. Driving roller.-   12 bis. Electrostatically charged driving roller.-   13. Film.-   14. “RIBI” film application device.-   19. Dielectric.-   20. Insulator.-   21. Opening edge.

1. A device for applying an extensible film onto an edge of an openingof a container comprising at least one compressed gas source, gas supplyfrom the gas source, one or more pipes for gas flow, and one or moresuitably oriented nozzles for blowing the gas between the edge of theopening and a surface of the film facing the edge, further comprising acapacitor of two or more plates disposed in the one or more gas pipes orbeing in contact therewith, and insulation for electrically insulatingthe capacitor from the device.
 2. The device of claim 1, wherein one ormore of the plates comprise electrostatic charge.
 3. The device of claim2, wherein one or more of the plates comprise one or more tips disposedin the gas pipe.
 4. The device of claim 3, wherein the tips are orientedin a flow direction.
 5. The device of claim 3, wherein the tips arecovered with noble metal.
 6. The device of claim 2, wherein the platesare connected to one or more plates of an additional electric capacitor.7. The device of claim 6, wherein the plates are connected to electricresistors or rheostats.
 8. The device of claim 1, further comprising oneor more heating bodies disposed in a tank for feeding gas coupled to theone or more gas pipe.
 9. The device of claim 8, wherein the one or moreheating bodies is controlled by one or more thermostats.
 10. The deviceof claim 1, further comprising at least one suitable steam generator, atleast one suitably heat-insulated pipe, one or more adjustable nozzlesfor blowing the gas.
 11. The device of claim 10, wherein the one or morenozzles further comprise suitable opening and closing valves.
 12. Thedevice of claim 11, wherein the nozzles further comprises one or moreflow control valves.
 13. The device of claim 10, further comprising oneor more thermostats.
 14. The device of claim 10, wherein the steamgenerator is a dry steam generator.
 15. A device for applying anextensible film onto an edge of an opening of a container comprising atleast one compressed gas source, gas supply from the gas source, one ormore pipes for gas flow, and one or more suitably oriented nozzles forblowing the gas between the edge of the opening and a surface of thefilm facing the edge, further comprising a capacitor having one or moreelectrically chargeable plates disposed in or around the pipe.
 16. Thedevice of claim 15, further comprising one or more additional electriccapacitors.
 17. The device of claim 16, further comprising electricresistors or rheostats.
 18. The device of claim 15, wherein the platescomprise one or more tips disposed in or around the pipe.
 19. The deviceof claim 15, further comprising one or more suitable radiant heatsources disposed at or near the edge of the opening.
 20. The device ofclaim 19, wherein the heat sources are disposed proximal the extensiblefilm.
 21. A device for applying an extensible film onto an edge of anopening of a container comprising at least one compressed gas source,gas supply from the gas source, one or more pipes for gas flow, and oneor more suitably oriented nozzles for blowing the gas between the edgeof the opening and a surface of the film facing the edge, furthercomprising one or more suitable radiant heat sources disposed at or nearthe edge of the opening to be sealed, wherein the heat sources aredisposed proximal the extensible film, further comprising a charger forreleasing electric charges to the edge of the opening to be sealedand/or to the extensible film by corona discharge.
 22. The device ofclaim 21, wherein the charger comprises one or more suitable insulatedconductors at high electromotive voltage appropriately positioned by theedge of the opening to be sealed and/or the extensible film to beapplied.
 23. The device of claim 21, wherein the container is selectedfrom the group consisting of plastic, polymer, metal containers, andcombinations thereof.
 24. The device of claim 21, wherein the film is apolymer film.
 25. The device of claim 21, wherein the container is abottle.